1. Field of the Invention
The present invention relates to a wrench with a fixed maximum operational torque to prevent damage to the object secured by a fastener driven by the wrench.
2. Description of the Related Art
FIG. 16A of the drawings illustrates a conventional wrench 1 having a hexagonal driving portion with six planar faces 2 for engaging with six faces of a hexagonal groove in a top face of a fastener. However, slide tends to occur between the planar faces of the driving portion of the wrench 1 and the faces of the fastener. FIG. 16B illustrates a so-called TROX wrench 3 having plural arcuate faces 4 for engaging with corresponding arcuate faces in a top face of a fastener. Such a TROX wrench 3 is used to tighten important parts of a car and cutting tools. As illustrated in FIG. 17, a blade 7 is tightened to a cutting tool 5 by a bolt 6. However, the expensive blade 7 tends to be damaged when the bolt 6 is excessively tightened. But the blade 7 could fly away and thus cause injury if the bolt 6 is not tightened to the desired extent.
An object of the present invention is to provide a wrench with a fixed maximum operational torque such that when the torque applied by the user is greater than the maximum operational torque, the wrench slides and the fastener is not turned. Thus, damage to the object secured by the fastener resulting from over-tightening is prevented.
Another object of the present invention is to provide a wrench with a fixed maximum operational torque that can be altered in response to the actual use.
In accordance with one aspect of the present invention, a wrench comprises a rod, a retainer, and a casing for accommodating the retainer and allowing relative pivotal movement between the casing and the retainer. The rod comprises a driving portion on an end thereof for engaging with a fastener. The retainer has a first end securely mounted to the rod to turn therewith and a second end. An engaging member is mounted in the casing and biased to engage with the second end of the retainer, thereby exerting an engaging force between the second end of the retainer and the engaging member. When a rotational force applied to the casing is smaller than the engaging force, the retainer and the rod are turned to thereby turn the fastener. When a rotational force applied to the casing is greater than the engaging force, the casing slides relative to the retainer while the retainer and the rod are not turned.
In accordance with a second aspect of the invention, a wrench comprises a rod, a retainer, and a casing. The rod comprises a driving portion on an end thereof for engaging with a fastener. The retainer has a central portion securely mounted to the rod to turn therewith and two ends. The casing accommodates the retainer and allows relative pivotal movement between the casing and the retainer. Two engaging members are mounted in the casing and biased to respectively engage with the ends of the retainer, thereby exerting an engaging force between each of the ends of the retainer and an associated one of the engaging members. When a rotational force applied to the casing is smaller than the engaging force, the retainer and the rod are turned to thereby turn the fastener. When a rotational force applied to the casing is greater than the engaging force, the casing slides while the retainer and the rod are not turned.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.